This invention relates generally to high frequency synthesizers. High frequency synthesizers are now commonly utilized substitutes for the crystal controlled transmitter oscillators and receiver local oscillators because they are able to provide a frequency stable signal at any one of a plurality of frequencies without the need of a crystal for each such frequency. Such synthesizers generally utilize a phase-locked loop including a voltage controlled oscillator (VCO), a reference oscillator, and a phase detector for comparing the output of the VCO with a reference source. Normally, one or more programmable or switchable multipliers or dividers are included within the phase-locked loop so that the loop can be locked to various multiples of the reference source frequency.
As high frequency synthesizers have become widely utilized, they have even been incorporated into portable or mobile battery powered radio communication equipment, such as cellular type radio telephone equipment. It has been found, however, that during normal operation, the phase-locked loop of a synthesizer requires substantial power to operate. Cellular radio equipment must spend large amounts of time receiving a signalling channel. During such reception, the phase-locked loop of its synthesizer is normally continuously operated. Under such operating conditions, the high power drain associated with the synthesizer expends the available battery power in an impractically short period of time.